Slot dies are used for applying thin fluid coatings across a wide range of substrates, and can include single-layer or multi-layer dies. A single-layer slot die applies a single layer of fluid onto a substrate, whereas a multi-layer slot die applies at least two layers of fluid onto a substrate. The fluid is forced out of a reservoir through a slot to a lip face by pressure, and transferred to a moving substrate. Generally, the slot is significantly smaller in section than the reservoir and is oriented perpendicular to the direction of substrate movement.
To change the amount of fluid being applied to the substrate, the size of the slot can be adjusted. Different thicknesses of shims placed between two body sections or a mechanical slot adjustment are used to increase or decrease the size of the slot. A thick shim can be used to increase the size of the slot, and conversely, a thin shim can be used to decrease the size of the slot. In conventional multi-layer slot dies, if the size of one or more of the slots is adjusted by a shim, the lip face where the fluid is extruded becomes offset. An operator must then use a chart or calculation to eliminate or compensate for the lip face offset. Also, since the plane of the offset surface is perpendicular to the mating surface of the body sections and not parallel to the lip face, the operator must also calculate the offset shim thickness to achieve the desired lip offset. This process can be time consuming and requires additional equipment to ensure that the slot die maintains a desired lip offset.
Therefore, there is a need for an improved slot die and method for adjusting the coating gaps and lip offsets within the slot die.